According to Ullmann's Encyclopedia of Ind. Chem., Vol. A24, 107 (1993), silver is a precious metal resistant to oxidation, with superior electrical and thermal conductivity and catalytic and antibiotic activity. Thus, silver and silver compounds are widely used in alloys, plating, medicine, photography, electricity and electronics, fibers, detergents, household appliances, and so forth.
Silver compounds can be used as catalyst in synthesis of organic compounds and polymers. Especially, with the recent regulation of use of lead in electric and electronic circuits, use of silver in low-resistance metal wirings, printed circuit boards (PCB), flexible printed circuit boards (FPC), antennas for radio frequency identification (RFID) stags, plasma display panels (PDP), liquid crystal displays (TFT-LCD), organic light emitting diodes (OLED), flexible displays and organic thin-film transistors (OTFT) as metal patterns or electrodes is on the increase.
Mostly, silver is used in the form of a paste comprising silver powder, a binder and a solvent. Or, a silver compound such as silver nitrate is reacted with another compound in an aqueous solution or an organic solvent to obtain a variety of silver compounds or organic silver compounds containing nanoparticles. These organic silver compounds are used to form metal patterns by chemical vapor deposition (CVD), plasma vapor deposition, sputtering, electroplating, photolithography, electron beam technique, laser technique, etc.
The most common coordinator for organic silver complexes is carboxylic acid (Prog. Inorg. Chem., 10, p. 233 (1968)). However, because silver-containing metal carboxylate complexes are generally sensitive to light, hardly soluble in organic solvents (J. Chem. Soc., (A), p. 514 (1971), U.S. Pat. No. 5,534,312 (Jul. 9, 1996)) and have a high decomposition temperature, they are limited in application in spite of easiness in preparation. To solve this problem, several methods have been proposed in J. Inorg. Nucl. Chem., 40, p. 1599 (1978), Ang. Chem., Int. Ed. Engl., 31, p. 770 (1992), Eur. J. Solid State Inorg. Chem., 32, p. 25 (1995), J. Chem. Cryst., 26, p. 99 (1996), Chem. Vapor Deposition, 7, 111 (2001), Chem. Mater., 16, 2021 (2004), U.S. Pat. No. 5,705,661 (Jan. 6, 1998) and Korean Patent No. 2003-0085357 (Nov. 5, 2003). Among them are the methods of using carboxylic acid compounds having long alkyl chains or including amine compounds or phosphine compounds. However, the silver derivatives known thus far are limited and have insufficient stability or solubility. Moreover, they have a high decomposition temperature to be applied for pattern formation and are decomposed slowly.
U.K. Patent No. 609,807 published in 1948 discloses a method of reacting ammonium carbonate or ammonium carbamate with a transition metal salt to obtain a transition metal salt coordinated by ammonia as carbon dioxide is generated. The patent mentions that silver complexes coordinated by ammonia can be prepared by the method. However, surprisingly, the present inventors found out that when ammonium carbonate or ammonium carbamate is added to a silver compound such as silver oxide, a stable silver complex is obtained without generation of carbon dioxide. They also confirmed that the silver complex is isolated as solid and can be easily prepared into thin film.
The silver complexes of the present invention are characterized in that, because they can be prepared under various reaction conditions, they have superior stability and solubility, can be easily prepared into thin film, thus enabling ease metal patterning, and are decomposed at low temperature, thus being easily prepared into thin film or powder.